The present invention relates to an apparatus for inter-connecting optical devices and, more particularly, to a connector for terminating an optical fiber.
Optical fiber connectors are an essential part of substantially any optical fiber based communication system. For instance, such connectors may be used to join segments of fiber into longer lengths, to connect fiber to active devices such as transceivers, detectors and repeaters, or to connect fiber to passive devices such as switches and attenuators. The central function of an optical fiber connector is to maintain or position two optical fiber ends such that the core of one fiber is axially aligned with the core of the other fiber. Consequently, the light from one fiber is coupled to the other fiber or transferred between the fibers as efficiently as possible. This is a particularly challenging task because the light-carrying region or core of an optical fiber is quite small. In single mode optical fibers, the core diameter is about 9 microns. In multi-mode fibers, the core can be as large as 62.5 to 100 microns, and hence alignment is less critical. However, precision alignment is still a necessary feature to effectively interconnect the optical fibers.
Another function of the optical fiber connector is to provide mechanical stability to and protection for the optical junction in its working environment. Achieving low insertion loss in coupling two fibers is generally a function of the alignment of the fiber ends, the width of the gap between the ends, and the optical surface condition of either or both ends. Stability and junction protection is generally a function of connector design (e.g., minimization of the different thermal expansion and mechanical movement effects). Precision alignment of the optical fiber is typically accomplished within the design of the optical terminus assembly. The typical optical terminus assembly utilizes a method of retention of the terminus within the connector(s) integrated within it and a method of holding and aligning the optical fiber. To align the optical fiber, a terminus typically includes a small cylinder of metal or ceramic at one end commonly referred to as a “ferrule.” The ferrule has a high precision hole passing along it centerline and glass or plastic optical fiber can be installed into the hole within the ferrule using mechanical, adhesive or other retention methods. The primary operational sections of an optical terminus are the support structure around the ferrule and the mechanism (typically a spring) used to create a force to push the ferrule into an opposing ferrule of a mating optical connector.
In a connection between a pair of optical fibers, a pair of ferrules is butted together in an end to end manner and light travels from one to the other along their common central axis. In this conventional optical connection, it is highly desirable for the cores of the glass fibers to be precisely aligned in order to minimize the loss of light (such loss being referred to as insertion loss) caused by the connection. As one might expect, it is presently impossible to make a perfect connection. Manufacturing tolerances may approach “zero” but practical considerations such as cost, and the fact that slight misalignment is tolerable, suggest that perfection is unnecessary although stability across the operating environment of the fiber joint is critical.
Historically, due to manufacturing costs and design features, optical termini have tended to be manufactured as an assembly of loose components. In high performance connectors intended for single mode application, there exists a specific need to tune out the eccentricity of assemblies and such tuning has been achieved by the interaction between the terminus or ferrule support structure and the connector housing. This is an undesirable effect as the housing becomes an integral element in tuning and if the terminus is removed from the housing (such as for cleaning or replacement), the tuning is in effect lost.
Optical terminus assembly tuning is used to reduce the random position of the optical fiber within an optical connector. The randomness of this positioning may be in the order of fractions of microns to several microns. However, when consideration is taken of single mode optical fiber with an optical waveguide of only 8-9 microns in diameter, it can be seen how optical insertion loss can be dramatically impacted if control of the placement of the optical core is not maintained. Fiber eccentricity compensation is currently most commonly found on single channel “LC” style connectors. Compensation is attained using a faceted structure (such as a square or hexagon) to register on the front end of the ferrule support structure. The support structure engages an appropriate complementary pattern within the LC connector body and retains positioning by engaging the LC body. Thus tuning or fiber eccentricity compensation is only retained as the ferrule and its support is retained within the connector body. Once removed it is not possible to determine the exact positional relationship between the fiber holding structure and the connector body.
Recognizing the engineering challenge posed by the alignment of two very small optical fiber cores, it is desirable to provide termini that are smaller, less expensive, and yet more convenient for customers to manipulate. One of the key features associated with the design of termini is the system for retaining the termini in a connector. The retention feature affects the ability of the terminus to be engaged into a connector system and retained within the connector system during mating of the two connector halves. The retention system must enable users of the optical terminus system and its associated connector system the ability to remove the optical termini individually for service, repair, inspection or other reasons. Existing optical termini systems are typically utilized in military connector systems and some designs incorporate anti-rotation features but none include an operative retention system and tuning capability as an integral part of the terminus.